Add cli notes.

readme.md

@@ -39,8 +39,17 @@ lighthouse --help
 git clone https://github.com/GoogleChrome/lighthouse
 cd lighthouse
 npm install
+
+cd lighthouse-core/
+npm i
 ```
 
+#### Working on the CLI.
+
+The CLI is implemented in typescript as part of an experimental branch of the source code. Due to this fact you must run a filewatcher and compile step during development.
+
+This is as simple as `npm run dev`
+
 #### Run
 
 ```sh